1. Field of the Invention
The present invention relates to a detecting circuit and method for pulse frequency modulation, and more particularly, to a circuit and method for detecting the maximal frequency of the pulse frequency modulation.
2. Description of the Related Art
FIG. 1 is a hint diagram of a prior art pulse frequency modulation. The frequency of a prior art pulse frequency modulation is determined by its workload. The heavier the workload is, the higher the operating frequency will be. In FIG. 1, TON represents the pulse width of the pulse frequency modulation signals, and TOFF represents intervals between the pulse frequency modulation signals. The smaller the parameter TOFF is, the higher the operating frequency will be.
FIG. 2 is an enlarged diagram of a prior art pulse frequency modulation. In practical applications, the pulse frequency modulation signals generated by the oscillator are usually triangle waves, while the TON pulses shown in FIG. 1 are only the first-half cycles of the pulse frequency modulation signals. If TOFF is equal or close to zero, it represents the fact that the maximal frequency of the pulse frequency modulation signals has appeared already, and at this moment the pulse frequency modulation signals are in a continuous state.
For some applications, the pulse frequency modulation signals at the position of the maximal frequency have a very high utilization value. Therefore, the method needed to detect if the maximal frequency already appeared is an important issue.